Isotopic analysis of δ¹³C in apple and grape products

Isotopic analysis is an effective technique for verifying the authenticity of food, allowing the identification of adulteration with precision. The δ¹³C values in sugars and organic compounds reflect photosynthetic metabolism: C₃ species, such as apples and grapes, have more negative values, while C₄ plants, such as corn and sugarcane, have more positive values. This differentiation makes it possible to identify fraud involving sugars of C₄ origin in products derived from fruits, in addition to assisting in traceability and the definition of reference values. The objective of this study was to evaluate the isotopic variation of δ¹³C in apple and grape products, seeking to identify natural patterns and signs of adulteration. A total of 604 isotopic values obtained between 2020 and 2024 were analyzed, including: clarified apple juice (n=85), fermented apple juice (n=40), apple nectar (n=10) and apple cider vinegar (n=96); and, for grapes, whole juice (n=172), nectar (n=18), wine vinegar (n=39), dry (n=130) and mild (n=14) wines. The analyses were performed by isotope ratio mass spectrometry at the Center for Stable Isotopes of UNESP. The results indicated greater isotopic variation in nectars, vinegars and clarified apple juice, with less negative values, suggesting the presence of C₄ sugars. In nectars, this characteristic is compatible with the legislation, which allows the addition of sugars as long as there is at least 30% juice. The fermented apples and wines showed more consistent isotopic values, close to those expected for C₃ species, reflecting greater authenticity in the origin of the sugars